1. Field of the Invention
The present invention relates generally to a control system for an internal combustion engine, and more particularly to, a method of controlling a purge solenoid for a control system of an internal combustion engine.
2. Description of the Related Art
Under normal operating conditions, fuel vapors form inside an automotive vehicle's fuel tank. These vapors are temporarily stored inside of a vapor storage canister. These containment devices are also known as purge canisters, vapor canisters, and the like. A typical purge canister contains a quantity of activated charcoal as the preferred medium for storing the fuel vapors. Because the purge canister's storage capacity is limited by the charcoal becoming saturated with absorbed fuel vapor, it is necessary to purge the canister with fresh air to remove the fuel vapor.
Typically, a control system is used to purge the canister. The control system includes a purge solenoid which is turned ON and OFF to control fuel vapor purged from the purge canister. An example of such a control system is disclosed in U.S. Pat. No. 4,821,701 to Nankee II et al., the disclosure of which is hereby incorporated by reference. Although this control system has worked well, there is still a need to control and vary the amount of purge flow from the purge canister to the internal combustion engine.